1. Field of the Invention
This invention relates to a process for heat-treating certain alloys within critical process parameters to increase the hydrogen embrittlement resistance of the alloys and to the improved alloys resulting from the application of the process.
2. Description of the Prior Art
A major obstacle to successful drilling and completion of deep wells for oil and gas is hydrogen sulfide. When oil or gas is contaminated with hydrogen sulfide they are referred to as sour, and these sour environments cause a number of problems. A principal problem associated with these sour environments is their tendency to cause brittle failure of the metals used in drilling and completing the wells. This brittle failure can be a problem particularly when using the high strength alloys needed for producing deep high pressure sour wells.
Brittle failure has been experienced with tubing, casing, drill pipes, wire lines, and related equipment. Sudden failure of such equipment can occur with little visible corrosion and no detectable plastic deformation. Moreover, brittle failures can occur in metals subjected to apparently safe loading and often after extended periods of satisfactory service. Such failures can result in loss or blowout of the well with disastrous consequences in terms of life and money.
Although the mechanism of such brittle failure is not fully understood, it is believed to be caused by entry of atomic hydrogen (H) into the metal. Hydrogen drastically reduces the ductility and causes the metal to crack. This phenomenon is commonly called hydrogen embrittlement. The mechanism of hydrogen embrittlement is more complex in the presence of hydrogen sulfide because of additional chemical reactions. In the presence of hydrogen sulfide, this mechanism is commonly called hydrogen sulfide embrittlement or sulfide stress cracking. The term hydrogen embrittlement, however, will be used herein in reference to brittle failure regardless of the hydrogen source.
Hydrogen sulfide is one source of the hydrogen and a common one. It may originate from water containing sulfur compounds, inflow of formation fluids, bacterial action on sulfates in drilling fluids, thermal degradation of drilling fluid additives and chemical reactions between sulfur compounds and metal. Hydrogen itself rather than hydrogen sulfide may be the cause of the brittle failure. Uncombined hydrogen can be generated from a number of sources including corrosion processes in the drilling fluids, bacterial action, and thermal degradation or organic additives.
Further discussion of hydrogen embrittlement problems is described in the following references.
Greer, J. B., "Metal Thickness and Temperature Effects in Casing and Tubing Design for Deep, Sour Wells", paper SPE 3968, presented at the SPE-AIME 47th Annual Fall Meeting, San Antonio, Tex., Oct. 11, 1972. PA0 Watkins, M. and Greer, J. B., "Corrosion Testing of Highly Alloyed Materials for Deep Sour Gas Well Environments", paper SPE 5622, presented at SPE-AIME 50th Annual Fall Meeting, Dallas, Tex., Sept. 28-Oct. 1, 1975. This paper pointed out "the need to safely produce gas from deep (20,000 ft), high pressure (20,000 psi), high temperature (400.degree.-500.degree. F.) reservoirs containing high percentages of H.sub.2 S and CO.sub.2 along with salt water." PA0 Greer, J. B., "Factors Affecting the Sulfide Stress Cracking Performance of High Strength Steels", Materials Performance, Vol. 14, pp. 11-22, January 1975. PA0 Kane, R. D. and Greer, J. B., "Sulfide Stress Cracking of High-Strength Steels in Laboratory and Oilfield Environments", paper SPE 6144, presented at SPE-AIME 51st Annual Fall Meeting, New Orleans, La., Oct. 3-6, 1976. PA0 Kane, R. D. and Greer, J. B., "Embrittlement of High-Strength, High-Alloy Tubular Materials in Sour Environments", paper SPE 6798 presented at SPE-AIME 52nd Annual Fall Meeting, Denver, Colo., Oct. 9-12, 1977. PA0 Bates, T. R., "New Alloys for Use in High Pressure, Sour Gas Wells", Graduate Seminar at the University of Houston presented on Oct. 21, 1977. PA0 Tuttle, R. N. (Shell Oil Co.) and Kochera, J. W., EFFECT OF HYDROGEN ON BEHAVIOR OF MATERIALS [Book] Metallurgical Soc. of AIME, New York; pp. 531-541, 1976; Abstr. No. 28784, ERDA ENERGY RES. ABSTR. v. 2, No. 12, p. 2953, June 30, 1977. PA0 Nielsen, N. A. (du Pont de Nemours & Co.); "Stress Corrosion Cracking and Hydrogen Damage", MATER. PROBL. & RES. OPPORTUNITIES IN COAL CONVERSION WORKSHOP (Columbus, Ohio, 4/16/74) PROC. v. 2, pp. 397-418 [n.d.] (CONF-740473--P2); Abstr. No. 00138, ERDA REP. ABSTR. No. ERA 75/2, p. 7, April 1975.
U.S. Pat. No. 4,057,108 entitled "Completing Wells in Deep Reservoirs Containing Fluids That are Hot and Corrosive" highlights the intensely corrosive environment that alloys are subjected to in deep sour gas wells, but offers no suggestion for improving alloys. It does suggest the use of Multiphase MP35N alloy (available from Standard Press Steel Company).
U.S. Pat. No. 3,645,726 entitled "Resistance to Stress-Corrosion Cracking in Nickel Alloys" was previously cited by the Examiner in a parent application and does not teach the critical temperature limitations found by Applicants to give the superior alloy properties.
Several suggestions have been proposed to minimize equipment failure caused by hydrogen embrittlement. For example, inhibitor additives, protective coatings and metallurgical compositions have been proposed. Among the more promising metallurgical compositions proposed for use in deep sour wells are the highly alloyed metals such as high-strength super austenitic stainless alloys composed principally of nickel (and/or cobalt), chromium and molybdenum.
Other proposed methods to reduce embrittlement problems in conventional steel or alloy components include contacting the metal equipment with hydrogen sulfide at temperatures above 150.degree. F., avoiding use of pipe that has been cold-straightened or cold-worked, using biocides to control sulfate reducing organisms, maintaining a high pH (9-10.5) within the well and using thicker wall pipe to reduce high stresses. Although the oil and steel industries have made significant efforts to resolve the hydrogen embrittlement problems of steels, most of the proposed methods are essentially ineffective to totally protect metal equipment from brittle failure.
As wells are drilled deeper and as higher concentrations of hydrogen sulfide are encountered at higher pressures, there is a substantially unfilled need for high-strength tubing material which has improved resistance to hydrogen embrittlement.